The aim of this project is to develop a physiological wireless monitoring device that is small enough to be worn by a mouse or juvenile rat. This device will allow behavior to be observed and physiological parameters to be measured without tethering the rodent as is traditionally required. The Phase I of this program developed a small, two channel wireless physiological monitor transmitter that allows EEG, EKG, EMG and other physiological parameters of rats and other small animals to be measured by researchers. The Phase I developed a transmitter, which is small enough to be worn by a rat, and demonstrated the feasibility of such a device. It contains a data acquisition section, a digital section, and a programmable RF transmitter section. It is packaged in a silicone dip, which will protect the device from urine and other fluids as well as from electric shock. It has been tested on rats at John Hopkins Medical Institutions. In Phase II, the transmitter will be shrunk to allow it to be used for developing rats or mice environments. The transmitter will have sufficient range to allow the animals to freely move about their environment, which will allow for free maze studies, and even mazes that include navigating through water. Testing on the RatPaak will be continued at Johns Hopkins during the Phase II as well as testing on the newly developed MousePaak.